1. Introduction to Zeolites

2. A three-letter code system has been developed for naming, assigned to specific structure types independent of their actual chemical compositions
e.g., the code LTA is used for Zeolite A and is derived from the name Linde Type A.

3. Bronsted Acidity
Al – OH – Si Terminal Silanol group
Lewis Acidity
AlO+ , Al(OH)3 x H2O Metal Cations

4. Few common STRUCTURES

5. Cation exchange properties of zeolite is function of its intrinsic properties :
Framework topology
Ion size and shape
Charge density of anionic framework
Ion valence
Electrolyte concentration in aq. Phases

6. Characteristics and Physicochemical properties of Zeolites
High surface area,
Uniform micropore size,
High hydro thermal stability,
Intrinsic acidity,
Ability to accommodate active metal species,
Introducing constraints to undesired species by molecular sieving effect (shape selectivity),
Environmentally harmless,
Non-corrosive,
Show ease of separation from reaction mixture compared with homogeneous catalysts.

7. Zeolites used as FCC catalysts
Zeolites typically applied as FCC catalysts are Type X, Type Y and ZSM-5
X zeolite has a lower silica-alumina ratio, which makes it less stable.
ZSM-5 is a versatile zeolite that helps in increasing the yield of olefins from FCC.
Zeolite Y
Zeolite X

8. Synthesis of FCC Catalysts

9. Inside FCC Catalyst

10. Major Physical Characteristics of FCC Catalysts
Attrition Resistance :
High gas flow rates and the harsh temperature  attrition of the catalyst particles and produce fines.
An increased zeolite content of the catalyst, reduction of the zeolite crystal size and better dispersion of the zeolite within the matrix
Pore Size Distribution and Pore Volumes :
Small pores  greater tendency to get clogged by coke
greater diffusional resistance
Surface Area:
The surface area of the catalyst comes from the zeolite and also the matrix.
It ranges from 600 – 800 m2/gm in zeolites

11. Size Constraints or Molecular sieving or Shape selectivity
Due to rigid skeletal system, zeolite window has intact window size due to which molecules having size larger than this window dimensions often experience constraints in accessing the intrinsic sites.
Thus, prevents undesired large molecules to enter network.
Shape selective

12. (1) Reactant Shape selectivity
This refines the accessibility molecules inside pore geometry of zeolite by imparting the fixed window opening, thus limits the diffusion of molecules with kinetic diameter larger than this window.
This allows shape selective entrance of molecules, activity of such molecules is often hindered.
Fig Shows the shape selectivity of n- butane and iso-butane over zeolites.
Fig. Shape selectivity of Hydrocarbons Reactants on to zeolite framework

13. (2) Transition Shape selectivity
Transition shape selectivity refers to curbing of intermediate compounds formed therin the framework whose size is larger than skeleton size.
Fig. shows formation of small sized isomer compared to bulky ones.
Fig. Shape selective transition
compound formation restriction

14. (3) Product Selectivity
Due to restricted pore size products diffusing through these materials experience constraints and so product formed is also selective in nature.
But however sometimes this bulky products accumulate over a position of zeolite blocking the accessibility of virgin molecules resulting into coking or deactivation of catalyst.
Fig. 8 Shape selective product formation.

15. Mesoporous M41S Materials
Lamellar MCM-50
Hexagonal MCM-41
Cubic MCM-48 8

16. More resistant to pore blockages
What makes MCM-48 interesting candidate ?
Three dimensional interwoven structure
More resistant to pore blockages
High surface area, pore volume and thermal stability
Higher catalytic activity than one dimensional counterpart, MCM-41.
Structures of MCM-41 and MCM-48 12

17. Zeolites used as FCC catalysts
Zeolites typically applied as FCC catalysts are Type X, Type Y (Faujasite Type) and ZSM-5
X zeolite has a lower silica-alumina ratio, which makes it less stable.
ZSM-5 is a versatile zeolite that helps in increasing the yield of olefins from FCC.
Zeolite Y
Zeolite X

18. Acidity Characterization
Name of reaction
Description
Solid-acid catalyst
used
Cracking/ hydrocracking
Crack large molecules in petroleum oils
FCC additives for more C3 and octane
Silica-alumina; ZeoliteY ZSM-5
Dewaxing
Crak n-paraffins (waxes) in petroleum oils
ZSM-5
Isodewaxing
Isomerization of waxy molecules.
SAPO-11
Xylene isomerisation
p- and o-xylenes from m-xylene.
ZSM-5; Mordenite
Naphtha reforming
Isomerization reactions for aromatization of paraffins.
Chlorided alumina
Hydrotreating
Remove N and S from petroleum oils
Alumina support
Hydration
Hydrate olefins to alcohols.
Ion-exchange resin; ZSM-5;

19. achieve maximum selectivity for the desired reaction
It is important to know the strength of the acid catalyst to
achieve maximum selectivity for the desired reaction